1. Field of the Invention
The present invention relates to signal processing apparatuses and techniques for suppressing cloud-clutter, but more specifically, it relates to an analog spatial filter subsystem and circuit configured for optimal performance of resolving targets against a cloud-cluttered background in an infrared search and track (IRST) system, which outputs data to the analog spatial filter subsystem and circuit in an analog format.
2. Description of the Prior Art
Infrared search and track (IRST) systems that are configured to operate in a sky-search mode need some type of cloud-clutter detection and discrimination capability to be able to resolve targets against a cloud-cluttered background while substantially eliminating false alarms. Considerable work has been done in this area. The results of a theoretical analysis has lead to the concept of the least-mean-square (LMS) spatial filter as one solution to the foregoing problem. In actuality, spatial filters discriminate between unresolved targets and background clutter on the basis of differences in the geometry between the targets and the background clutter. Because the assumptions concerning the nature of the target underlying the use of this class of filters are relatively mild, some form of spatial filter, for example digital, followed by a threshold test is nearly always used as a first level cloud-clutter discriminate.
In the prior art, many independent evaluations of various spatial filters have indicated the superiority of the LMS "filter". However, it must be realized that the LMS "filter" is defined by an impulse response, representing a formal solution to the classical match filter problem for arbitrary noise. In fact, a strict implementation is unrealizable, requiring infinite bandwidth circuits. Most attempts at approximate implementations of the LMS spatial filter have involved digital processing. Unfortunately, these methods require complex and costly hardware to handle the high data rates put out by high resolution IRST systems. Moreover, it is doubtful that digital implementations of the LMS "filter" will be able to handle the high data rates generated by the next generation of fast scan systems.